The present invention relates to a system which is capable of imparting a sufficient energy or power value to a multi-phase fluid comprising at least one gaseous phase and at least one liquid phase to transfer it from one location to another.
The system of the invention is based on an axial-flow (multi-phase) pump design which is adapted to a centrifugal pump and makes use of a synergetic effect combining the effects of each of the elements, which broadens the operating range and operation (gain in power or output) as compared with conventionally used pumping systems.
A system of this type will have the capacity to pump any type of effluent, irrespective of its gas to liquid ratio (GLR for short).
The concept axial-flow pump is also used to refer to multi-phase pumps adapted to pump fluids made up of several phases of different natures.
The present invention advantageously finds its application, although not exclusively so, in pumping from oil wells where the petroleum effluent consists of at least one gaseous phase and a liquid phase (made up of an aqueous phase and/or an organic phase, for example) and possibly solid particles.
With the methods of the prior art, a petroleum effluent is usually transferred from the bottom of the well to the surface by means of a centrifugal pump lowered into a bore and commonly known as a "down-hole pump". The majority of these pumps have several stages incorporating an impeller, the purpose of which is to impart a pressure-induced power and kinetic energy to the fluid, and an adjusting device whose function is to convert this high-velocity kinetic energy into a low-pressure energy bringing the fluid as close as possible to the axis or rotary shaft of the pump.
An impeller and an adjuster or diffuser represent one stage and throughout the description the word "stage" will be used to designate a unit consisting of a pair comprising an impeller and a diffuser, irrespective of whether the pump is of the axial or centrifugal type.
Similarly, the angles .alpha. and .beta. defined in the description below are considered with respect to a plane perpendicular to the axis of the rotation shaft.
In practice, centrifugal pumps have a disadvantage in that their operating range is limited. In effect, these pumps are suitable for compressing fluids which are essentially liquid but once there are more than a few percent of gas present in the fluid they no longer transfer energy to the fluid as well as they might.
The characteristics of pumping systems of the axial-flow type are such that energy is imparted to an effluent consisting of several phases of different natures, a gaseous phase and a liquid phase, but they are not capable of producing a gain in pressure per unit of identical length when the fluid is mainly in liquid form, such as that produced when using a centrifugal pump.